Comparative beetle emergence and root injury for rootworm-Bt traits in Cry3Bb1 problem fields in Illinois

The western corn rootworm is an important pest of corn and is widely managed through planting hybrids engineered to produce insecticidal toxins derived from Bacillus thuringiensis (Bt). The widespread planting of Bt corn places strong selection pressure on western corn rootworm populations. Field-evolved resistance was first suspected in Iowa fields as early as 2009. In 2011, fields were identified in Illinois where western corn rootworm larvae severely damaged Cry3Bb1 corn. Ensuing plant-based bioassays confirmed western corn rootworm resistance to the Bt toxin Cry3Bb1. Field experiments conducted in fields where Cry3Bb1 performance problems had been observed found increased root injury to Cry3Bb1 and mCry3A corn, as well as increased beetle emergence from Cry3Bb1 and mCry3A corn when compared to Cry34/35Ab1-containing corn. Additionally, we failed to document significant fitness costs associated with Bt resistance. This research demonstrates the vulnerabilities of planting Bt corn in problem areas and emphasizes the need for effective resistance management strategies to preserve the efficacy of Bt corn against the western corn rootworm.